This invention relates generally to a combustor of a turbine engine and, more particularly, to a combustor premixer.
In a typical aero-derivative industrial gas turbine engine, fuel is burned in an annular combustor. The fuel is metered and injected into the combustor by multiple nozzles along with combustion air having a designated amount of swirl. Non-uniformity of the fuel/air mixture causes the flame to be locally hotter, leading to significantly enhanced production of NOx. As herein used, the term "fuel/air mixture" is defined as a mixture of air and fuel for combustion.
In the typical turbine engine, flame stability and engine operability dominate the combustor design requirements. These requirements have in general resulted in combustor designs with the combustion at the dome end of the combustor proceeding at the highest possible temperatures at stoichiometric conditions. Additionally, designs that optimize flame stability and engine operability typically do not minimize production of NOx.
To reduce the production of NOx, hollow vane mixers have been used for fuel injection. Such a mixer includes an outer annular swirler and an inner annular swirler. The outer annular swirler includes hollow vanes with internal cavities and gas fuel passages for injecting gas fuel into the air stream. Using such a mixer, the high pressure air and the fuel is uniformly mixed, resulting in reduced formation of pollutants when the fuel/air mixture is exhausted out the downstream end of the mixing duct into the combustor and ignited. Such hollow vanes are used in both single fuel and dual fuel mixers.
Although the above described mixer satisfies the technical requirements of very low emissions, the mixer is complex and costly to fabricate, particularly the hollow swirl vanes. The hollow vane fabrication process includes time-consuming, intricate machining processes which result in reduced manufacturing yield. Further, as compared to a solid vane swirler, the reliability of the hollow vane swirler is reduced due to the potential for cracking around the injection openings and in the vane walls.
It is desirable to reduce the cost and improve the reliability of mixers. Such a mixer, however, must maintain acceptable combustion performance and emission levels.